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Background: Myocardial inflammation and apoptosis are key processes in coxsackievirus B3 (CVB3)-induced acute viral myocarditis (AVMC). Accumulating evidence reveals the essential roles of long noncoding RNAs (lncRNAs) in the pathogenesis of AVMC. Here, we aimed to evaluate the biological functions of a novel lncRNA guanylate-binding protein 9 (lncGBP9) in AVMC progression and further explore its underlying mechanisms. Methods: Initially, mouse models of AVMC were constructed by CVB3 infection. The expression and localization of lncGBP9 in heart tissues were analyzed using RT-qPCR and FISH. Adeno-associated virus serotype 9 (AAV9)-mediated lncGBP9 knockdown was then employed to clarify its roles in survival, cardiac function, and myocardial inflammation and apoptosis. Moreover, the mRNA and protein levels of pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β) were detected by RT-qPCR and ELISA, and the regulation of lncGBP9 knockdown on the NF-κB signaling pathway was investigated by Western blotting. Using an in vitro model of HL-1 cardiomyocytes exposed to CVB3 infection, the effects of lncGBP9 knockdown on cell viability, inflammation, and apoptosis were further evaluated in vitro. Results: Increased lncGBP9 expression was detected in the heart tissues of AVMC mice and CVB3-infected HL-1 cells, and was mainly located in the cytoplasm. Knockdown of lncGBP9 remarkably alleviated the severity of AVMC in CVB3-infected mice, as verified by improved cardiac function, and reduced myocardial inflammation and apoptosis. Additionally, lncGBP9 knockdown suppressed the NF-κB signaling pathway and consequently reduced productions of pro-inflammatory cytokines in vivo. In vitro functional assays further confirmed that lncGBP9 knockdown promoted cell viability, inhibited cell apoptosis, and reduced pro-inflammatory cytokines release in CVB3-infected HL-1 cells through suppressing NF-κB activation. Conclusions: Collectively, lncGBP9 knockdown exerts anti-inflammatory and anti-apoptotic effects in CVB3-induced AVMC, which may be mediated in part via NF-κB signaling pathway. These findings highlight lncGBP9 as an attractive target for therapeutic interventions. [ABSTRACT FROM AUTHOR]